linux-kernel - Re: [Xen-devel] [PATCH] xen/apic: implement io apic read with hypercall

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Date:	Fri, 20 Apr 2012 14:20:17 +0100
From:	Andrew Cooper <andrew.cooper3@...rix.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	Lin Ming <mlin@...pku.edu.cn>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [Xen-devel] [PATCH] xen/apic: implement io apic read with hypercall

On 20/04/12 14:12, Ian Campbell wrote:
> On Fri, 2012-04-20 at 13:53 +0100, Andrew Cooper wrote:
>>> Under what circumstances can these hypercalls fail? Would a BUG_ON be
>>> appropriate/
>> -EFAULT, -EPERM, anything xsm_apic() could return (which looks only to
>> be -EPERM).
> So either the guest has called a hypercall which it is not permitted to
> or it has called it with invalid parameters of one sort or another. Both
> of these would be a code bug in the guest and therefore asserting that
> no failure occurred is reasonable?
>
> What could the caller do with the error other than log it and collapse?
>
>> The call into Xen itself will return 0 as a value if an
>> invalid physbase is passed in the hypercall.
>> So a BUG_ON() is not safe/sensible for domU.
> I think you have successfully argued that it is ;-)
>
> Ian.
>

So I have.  -EMoreCoffee

Yes - I meant to say that BUG_ON() was ok for domU.

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com

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